Considering that alot of CPU power will be used to power the A.I, you're a bit behind. But if the A.I is programmed to just take longer instead of cutting corners then you just have to wait longer for the A.I to take its turns (I think there will be an option to give additional CPU power to the A.I like there was in Twilight of the Arnor.)
You'll definetly get good performance on a high resolution (game is turnbased after all ) but there will be Shader 4.0 things which your card don't support. The games engine will scale the graphics according to your GPU so after release, Brad can (will) put up a video/image on how it runs'n'shows on maxquality.
....Wonder if my GeForce 8800GTS 512MB (G92) can max it....
The best bang for the buck right now (in Sweden atleast) is the GeForce GTX 460. Reference model is recommended since they blow the hot air OUT of the case. If you get another model, get a cooler that blows out the hot air.